The minimum dimension that a given photolithography process can resolve is alternatively called the minimum feature size or the critical dimension. The feature size is a parameter of interest because reductions in the feature size tend to improve speed performance of the IC. The feature size of a printed integrated circuit (IC) is not uniform. The printing process results in slight variations of the feature size from lot to lot, from wafer to wafer, and from device to device within each wafer. As a result, programmable logic ICs, such as field programmable gate arrays (FPGAs), may experience variations in performance and functionality due to variations or defects resulting from the manufacturing process.
As circuit designs continue to place increased speed and power efficiency requirements on target devices, it is increasingly important for developers to simulate and test circuit designs on target devices using precise power and delay specifications prior to design realization. Due to the measured differences between devices caused by random variations between different dies, manufactured dies are often tested and assigned a performance grade value based on a number of performance grade factors such as speed/delay, operating temperature, operating voltage, power usage, etc. These factors may be guaranteed to designers. The tested die are typically sorted, packaged, and labeled according to one or more performance grades, allowing die capabilities to be closely matched to application requirements. In this manner, lower performing dies may be sold at a discounted price for non-demanding applications.
One concern is that the package of dies having a low performance grade, once purchased or otherwise acquired, may be relabeled to indicate a higher grade and wrongfully resold as legitimate packaged dies. Although some of these relabeled packaged dies may initially operate correctly, others may not. For applications having requirements exceeding the original performance grade rating, the relabeled dies will likely exhibit a higher failure rate and/or shorter lifespan than that guaranteed for legitimate dies—causing damage to the manufacturer's reputation.
The present invention may address one or more of the above issues.